1. Field of the Invention
The present invention generally relates to communication systems, and more particularly, to a system and method for improving communications between a digital loop carrier (DLC) and a central office (CO).
2. Discussion of the Related Art
In recent years, telephone communication systems have expanded from traditional plain old telephone system (POTS) communications to include high-speed data communications as well. As is known, POTS communications include the transmission of voice information, as well as PSTN (public switched telephone network) modem information, control signals, and other information that is transmitted in the POTS bandwidth.
Prompted largely by the growth in Internet usage, the provision of XDSL services to customer premises has proliferated over recent years. In this regard, the descriptor xe2x80x9cxxe2x80x9d preceding the DSL designator is used to broadly denote a variety of DSL services, including ADSL, RADSL, HDSL, etc. As is known, xDSL transmissions are sent to customer premises over the same twisted pair cabling as POTS transmission are sent. Since XDSL transmissions are communicated in a frequency band that is separate and distinct from the POTS frequency band, transmitting both types of signals over the same cabling (even at the same time), generally is not a problem. Specifically, the POTS frequency band is defined between approximately DC and approximately 4 kHz, while xDSL frequency bands (although they vary depending upon the specific service) are generally defined by a lower cutoff frequency of approximately 26 kHz, and an upper cutoff frequency that depends upon the particular xDSL service. As will be used hereinafter, the term DSL will be used interchangeably with the term xDSL, and should be construed to generically reference any of the of the various DSL services.
As is known, DSL is an additional service the customer typically purchases from its local service provider. The local service provider typically charges an additional service charge for the provision of the service. Until recently, the additional service charges have been somewhat substantial, resulting in a general limitation of the service to business enterprises. However, the services are now becoming more affordable, and therefore in higher demand. This higher demand, however, is beginning to create problems due to the existing infrastructure. Indeed, due to the existing infrastructure of the telecommunications system, DSL services are frequently unavailable to a would-be subscriber.
To better appreciate problems associated with the current infrastructure, reference is made to FIG. 1, which is a block diagram of an existing prior art telecommunications system. The telecommunications system includes a central office 10 in communication with a plurality of customer premises 14, 16, 18, and 20 through a digital loop carrier (DLC) 12. As is known, a DLC is a telecommunications device that connects end users to a central office. Frequently, the end users connected to a central office through a DLC are usually located more than 18,000 feet away from the central office. DLCs consist of a box containing line cards that concentrate individual lines within a given area, and then send the traffic over a high speed digital connection to the CO 10. In this way, DLCs extend the reach of telecommunications services from a CO, beyond the reach of a typical local loop. DLCs are frequently used in office parks, housing developments, apartments, etc. to minimize the need to run local loops over several miles to the CO servicing area. This, in turn, minimizes the use of copper, as each of the copper wire pairs 30 can carry up to 24 digitized voice channels (up to 30 digitized voice channels in some countries outside the U.S.). Instead, local loops connect a cluster of homes or businesses to a remote terminal (the DLC), which in turn concentrates the traffic into a higher bandwidth for delivery to the CO.
The high speed digital connection 30 extending between the central office 10 and the DLC 12 typically includes a plurality of T1 (in the U.S.) lines or E1 (in Europe) lines. As is known, a T1 line operates at speeds of 1.544 Mbps, which is capable of carrying 24 voice channels. One very common configuration includes a DLC that is configured to service 96 users. Such a configuration requires four T1 circuits in order to allow all 96 users to simultaneously use the telephone system. In such a configuration, the high speed interface 30 between the DLC 12 and the central office 10 may comprise five T1 circuits. The fifth T1 circuit typically acts as a spare that may be utilized in the event of a line failure, noise, etc. The economics of utilizing five copper pairs (the T1 lines), in place of 96 copper pairs, while delivering identical service to the end user provides significant value to the telephone companies, particularly when the distances to the remote locations are lengthy.
In recent years, many installations have replaced the T1 circuits 30 extending between the central office 10 and the DLC 12 with fiber optic cables, which can provide tremendous bandwidth between the CO and the DLC. However, the cost of replacing these lines is quite expensive. Therefore, where possible, it is desired to avoid replacing the T1 lines with fiber optics.
Having described the infrastructure in a large percentage of the existing telecommunications systems, it can be appreciated that the bandwidth requirements for DSL services pose a significant problem to such a (copper/T1) system. For example, ADSL can provide downstream rates from 1.5 Mbps to 8 Mbps, and upstream rates from 64 kbps to 1.5 Mbps, over a copper wires in existing telephone systems. However, it should be readily appreciated that the existing T1 service interconnect 30 existing between central office 10 and DLC 12 cannot support the bandwidth demands of simultaneous use by multiple users at customer premises 14, 16, 18, and 20 of such DSL services. As is more particularly illustrated in FIG. 1, a customer premises 14 may include multiple telephones 22, 23 and one or more computers 21 that communicate over the same two wire pair 15 to the DLC 12. If the computer 21 is equipped with a DSL card, the frequency spectra of the communications that occur over the local loop 15 may be like that illustrated by reference numeral 25. Specifically, it may include a voice band 26 that extends from approximately dc to approximately 4 KHz. Likewise, it may include an upstream frequency band 27 that extends from 64 kbps to 1.5 kbps. It may further include a downstream frequency band 28 that extends from 1.5 Mbps to 4 Mbps. It is readily appreciated that the four or five T1 lines interconnecting the central office 10 to the DLC 12 cannot support the full bandwidth capabilities of DSL, if multiple users within the various customer premises are attempting to carry on data communications over the Internet.
This problem may be manifest in either a significant data slowdown (from the stand point of the user). Alternatively, the service provider (central office) may simply inform customers that customer premises 14, 16, 18, and 20, that DSL services are not available for their customer premises. Certainly, with the growing demand for DSL services, there is a commensurately growing need for the service provider to enable the equipment to facilitate these services for the customer.
As previously mentioned, one approach is to replace the high speed communication link 30 between the DLC 12 and the central office 10 with fiber optic cabling. However, the cost of burying cable can be significant, particularly when there are significant distances separating the central office 10 from the DLC 12. An alternative solution is to provide individual local loops extending between the central office 10 and each of the customer premises 14, 16, 18, and 20. Again, burying or otherwise extending cable between the central office and the various customer premises sites is a relatively expensive solution. Furthermore, if the distance separating the central office from the various customer premises exceeds about 18,000 feet, then most DSL services cannot be adequately administered. As is known, due to the higher frequencies involved in DSL transmissions, the signal qualities significantly degradates beyond about 18,000 feet.
Accordingly, there is a present need and desire to provide an improved telecommunications system that accommodates high-speed communications with clusters of customer premises, including those more than approximately 18,000 feet from the central office.
Accordingly, it is desired to provide a networked computer system having the single DSL connection/service benefits of the system FIG. 1, but providing greater simplicity and user-friendliness from the end-user perspective.
Certain objects, advantages and novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the objects and advantages of the present invention, the present invention is directed to a system and method for upgrading a telecommunication system including a central office (CO), a digital loop carrier (DLC), and a plurality of customer premises equipment (CPE). Broadly, the present invention is realized by the retrofit of a DLC to enable the DLC to communicate with a CO through high bandwidth wireless transmissions. The high bandwidth wireless transmissions accommodate much larger data throughput than previously accommodated through the copper xe2x80x9cbackhaulxe2x80x9d of multiple T1 circuits.
In accordance with one aspect of the present invention, a telecommunications system comprises a CO, a DLC, and a plurality of CPE. Each of the plurality of CPE are electrically connected to the DLC. A radio frequency (RF) interface circuit is disposed at the DLC, along with one or more DSL line cards. A first wireless transceiver disposed at the DLC, and is electrically connected to the radio frequency interface circuit. A second wireless transceiver is electrically coupled to the CO. In accordance with the invention, information is exchanged between the CO and the DLC via wireless communications between the first wireless transceiver and the second wireless transceiver.
In accordance with a preferred embodiment of the present invention, the wireless transceivers communicate using a local multipoint distribution service (LMDS), operating preferably in a frequency range of approximately 27.5 GHz to 29.5 GHz. In one embodiment, the first wireless transceiver and the second wireless transceiver may be in direct communication with one another. In another embodiment, a third, and perhaps additional wireless transceivers may be interposed between the first wireless transceiver and the second wireless transceiver, whereby communications between the first wireless transceiver and the second wireless transceiver may be relayed through the third and other intervening transceivers.
In accordance with a similar, but alternative embodiment, the DLC may be disposed for wireless communication with a second DLC. The second DLC may, in turn, be disposed for communication with a CO via a fiber optic cable. In such an embodiment, a wireless transceiver need not be disposed at the central office.